Metal filament.



' WILLIAM I).

- ceedingly high temperature.

En srrarns rarnnr enri COOLIDGE, 0F SCHEN ECTADY, NEW YORK, ASSIGNOE T0 GENERAL ELECTRIC COMPA NEL A CORPORATION OF NEW YORK.

METAL FILAMENT.

No Drawing.

Specification of Letters Patent.

Application filed May 9, 1906. Serial No. 316,695.

To all whom itmay concern:

Be it known that I, WILLIAM D. CooLmsr,

a citizen of the United States, residing at ments, of which the following is a specification.

This invention pertains to the' art of incandescing conductors such as are used in electric lamps and other apparatus.

Many of the more refractory metals and elements have been suggested for use in incandescent lamps and in other apparatus where a conducting body is raised to an ex- Some of these refractory elements are, however, very difficult to shape into filaments because of the difiiculty of obtainin other slender conduc or. Tungsten is an example of this class of elements. It is ordinarily obtained as a fine powder, the particles of. which do not readily cohere and cannot be agglomerated into a coherent product vn'thout some special treatment.

According to this invention, a refractory material such as tungsten is incorporated in a metallic body, such as a ductile alloy, and the mixture so formed is shaped into a filament in any suitable way, and is then. treated to drive out all components except the refractory material, the latter remaining behind as a coherent product. Imay use various refractory metals or elements such as tungsten, molybdenum, boron, zirconium, titanium, thorium, tantalum, etc, and I may bind the separate particles of the powder together with various ductile alloys or metals.

I will explain the. process as applied to tungsten using a bismuth cadmium alloy as a binder, and it is to be understood that the same general process is applicable to other refractory metals, elements, and compounds, and that other binders may be used.

I purify the tungsten to make sure that -no impurities such as carbon are present.

I may also subject it to a special treatment to insure a very finely divided powder.

:Thisspecial process of *pulverizing or subdividing may consist in forming a colloidal solution in one of many well known ways,

and then driving off the liquid ofjthe solutionto leave behind fine particles of tungsten. The colloid may. be produced by forming an are between tungsten electrodes under 7 them in a wire or.

producing an alloy of a liquid, or may be made chemically and purified by-dialysis. 2

Still another method of insuring a fine powder consists in mixing the original powder with water, or other suitable liquid and allowing the powder to precipitate out. The fraction which comes out last is, of course, finerthan the part first precipitated. One of the advantages of having an exceedingly fine powder arises from the easewith which such a powder may be incorporated in another metal and squirted through a. very fine die to produce filaments of small cross section. Another advantage is the smooth surface which the filament has when very fine powder is used,

I next produce an alloy of cadmium and bismuth by meltin these two metals together over a gas ame orother source of heat. The proportions of the two components may vary, but good results may be' obtained by using 208 parts by weight of bismuth and 112 by weight of cadmium, thus roper proportions to satisfy the formula Big/d. I next heat some of this alloy to the plastic condition and rub into it the tungsten powder above mentioned. The exact proportion of tungsten to be added may vary between considerable limits; but if 53 per cent. by weight is used, the product can be readily manipulated and is otherwise satisfactory. This operation may be carried out b merely adding the tungsten to the alloy in a chemists mortar and rubbing the mixture with a pestle until it is homogeneous. I do not at present believe that the tungstencombines with the alloy, but think it is merely suspended and held together by the alloy acting as a binding agent. vThe tungstenma-y be added to the alloy and mixed therewith in the open air and the melting point of the alloy, about ltt centigrade, is not suficiently high to produce any oxidation of the tungsten. If

- I use some other binding metal or alloy having a melting point higher than that at which tungsten oxidizes in the open air,

then I find it desirable to perform this mix ing operation in an inert atmosphere or in a vacuum. The mixture of tungsten and mev tallic binding material above described. is next shaped into wires or filaments by squirting through a die. I find that I can squirt aments as fine as would probably ever be desired in electric lamps, or I can tungsten or such other refractory metal or metalsas may lave been used; or at least to drive outall the easily vaporizable materials. This may be. conveniently done by mounting the filaments in vacuum globes or in an inert atmosphere and passing current through the filaments to beat them. The easily va orizable components, such as bismuth an cadmium, come out very easily,-

and, so far as I have determined, very completely,-and leavebehind a coherent metallic product capable of operating at an exceed ingly hi h temperature and consequently at good lig t efiiciency. If desired, the distillation of the cadmium-bismuth alloy may be effected in a few moments, but I may heat for a much longer time to prevent a-sudden rush of vapors within the filament. After distillation is complete, I may heat the filament with current to a very high temperature to sinter together. the particles of tung-' 'have used the word metal sten or other refractory residue and improve the filament as a light giving conductor. The final product is a strong, uniform conductor, homogeneous in composition and very refractory.

In. certain of the claims appended hereto I p andI desire it to be understood that this term is used in the popular sense of either a metallic element, an alloy, or a metallic mixture.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. The composition consisting of a cadmium-bismuth alloy containing metallic tungsten.

2. The composition consisting of 8. bismuth alloy containing refractory metal.

3. The composition consisting of a cadvided refractory metal.

4. A conductive pliant wire consisting of fine particles held together by a cadmiumbismuth alloy adapted tobe converted into .a refractory incandescent body by suitable heat treatment. r 1

In witness whereof, I have hereunto set my hand this 8th 'day of May, 1906.

WILLIAM D. COOLIDGE.

mium-bismuth alloy containing finely di- \Vitness'es BEN AMIN B. HULL, Hanan Onronp. 

